Preparation of zinc-beryllium silicate phosphors



Patented Feb. 20, 1951 PREPARATION OF ZINC-BERYLLIUM SILICATE PHOSPHORS Jacob Roos, Eindhoven, Netherlands, assignor to General Electric Com New York pany, a corporation of No Drawing. Application December 8, 1947, Se-

rial No. 790,435. In the Netherlands January Claims. (Cl. 252-3015) My invention relates to luminescent materials generally, and more particularly to the preparation of fluorescent materials or phosphors of the zinc-beryllium silicate type.

Zinc-beryllium silicate activated with manganese; is an extensively used phosphor. This material is useful in gas or vapor discharge tubes in which it is excited to luminescence by ultraviolet radiations, as well as in cathode ray tubes in which it is excited to luminescence by electron bombardment. Widely varying proportions of the constituents have been proposed heretofore in various publications. The color of the luminescence may be varied within certain limits by a proper choice of the different proportions. Zinc-beryllium-manganese-silicate compositions have been compounded to produce yellow as well as red light. It has also been attempted, by varying the composition and particularly the proportion of the basic components to the silicic acid, to modify and improve other characteristics; for example, the luminous efliciency, the stability against the influence of the electrical discharge or electron bombardment, and the uniformity from batch to batch.

Inaccordance with processes referred to in the prior art literature a mixture of the oxides of zinc, beryllium, manganese and silicon is heated under certain conditions to a relatively high temperature, namely, about 1000 to 1300 C. Instead of the oxides, use may be made of materials which upon heating break down to yield the oxides; for example, carbonates or nitrates.

An object of my invention is to produce a product of high quantum efiiciency. Another object is to produce a product of greater stability or maintenance, particularly in mercury vapor discharge tubes, wherein the usual blackening is reduced considerably. Further objects and advantages of my invention will appear from the following description.

According to my invention, the luminescent zinc-beryllium-manganese-silicate is obtained, as hertofore, by heating a mixture of the components zinc, beryllium, silicon and manganese. However, I have found that the above-mentioned objectives may be attained by a modified procedure which involves two separate firing steps wherein at least a part of the total beryllium component is withheld from the mixture during the initial firing step and is subsequently added to the mixture for the re-firing step to produce the desired luminescent material.

According to one modification of the process comprising my invention the total necessary quantity of the beryllium component is added the diffusion process which produces the luminescent material it is only seldom possible to achieve a perfect equilibrium; in other words, that atoms remain on the surface of the luminescing crystals which have not yet found their exact place in the structure. It has been shown experimentally that this surface contributes most to the luminescence of the crystal. In accordance with the process comprising my invention, I obtain a crystal having a larger structure than the final product should have. This makes the crystallization easier, in addition to the fact that in the first phase or step of the process a relatively larger amount of silicic acid or silica is present than in the final product. The small beryllium ion has to be absorbed in the large crystal structure in the second phase or step of the process. However, it will be understood that the invention is not in any way limited by this explanation.

The following is an example of a particular composition which will illustrate the advantage to be obtained by this invention:

56.25 mol per cent ZnO- 3.1 mol per cent Mn 7.0 mol per cent BeO 33.6 mol per cent $102 By preparing this composition in accordance with the process heretofore employed wherein all the components were heated simultaneously, a quantum efficiency of was obtained. However, when the same material was prepared in accordance with a process comprising this invention, in which half the quantity of BeOl' was added in the first step and the remainder in the second step, a quantum efficiency of was obtained. These figures apply for the conversion of ultra-violet rays of 2537 A. into visible light at room temperature.

In a low pressure mercury vapor discharge tube, the wall of which was covered with this 111mb with the invention, a reduction of only.6%- occurred in thesame time;

For a further understanding of the invention,

the following example is given for the preparation of a particular luminescent zinc-beryllium- 'ox'ides, which comprises firing to reaction temmanganese-silicate l0667g. zinc oxide in the form of a zinc oxide solution; for instance, ZnO' dissolvedina solu-" tion of ammonia and ammoniumnarb'o'natex 400 g. manganese in the form of a manganese nitrate solution.

433 g. beryllium oxide in the formo-f a pure dry' material. 5167 g. silicic acid in the form of a partlyhye drolyzed ethyl silicate solution.

Thezinc oxide and the manganese nitrate solutionsarez'mixed in an evaporating dishwit-h half the quantity of the beryllium oxide. Then the ethyl silicate solution is added. After evaporationofzthe liquids in the bowl, during a period'of 20 hours, .for example, the remaining "material is The ground material .118 thenheated in an oven at about80'0 C. for about ground in a mortar.

sary.* The second half of the beryllium is then added and the mixture isrefired. The finalprod- 110131115131 material which I luminesces yellow-red when irradiated with rays of- 2537 A. from amercury vapor lamp,

The products made by the process comprising The reaction product steps, at least about half of the total beryllium component being withheld from the mixture during the initial firing step and being subsequently added to the mixture for the re-firing step.

2. The iprocess of preparing-luminescent manganese-activated zinc-beryllium silicate by the firing of a mixture of zinc, beryllium, silicon and .gmanganese components of the group consisting of the oxides of those components and materials which'iuponhe'ating break down to yield the said perature of about 1000-1300 C. in two separate Steps'pWhereinthe:mixture in the first step is composed of thezinc, silicon and manganese componentswhich. are fired to form a silicate compositionfafter which the necessary quantity of beryllium component is added and the composition is re-fired. V

sx'rhe process of preparing luminescent manganese-activated zinc-beryllium silicate by the firing of ai'mixture of zinc, bery1lium; siliconand manganese components of the groupiconsistin'gof the oxides of those components andima'terials which upon heating break down-to yield the said oxides, which comprises firing to ireaction tern perature of about 1000-1300" C. in two separate steps, whereinkthe mixture in the first step' isc composed'of the zinc, silicon and manganese;

components and about one-half of, the'neces -=sary beryllium component, which" are 'fired' to' form a silicate compositiom'after which-the" .re'-'- mainder "of the' necessary quantity of beryllium'-" component is added and the composition is" rethisxinventiorl may be used in mercury vapor tubes and in cathode ray tubes among others:

Theym'ay, if desired, be mixed with other luminescent materials, for example, with'm'aterials emitting blue light.

WhatI- claim: as new and'de'sire. to secure by Letters Patent of the United St'ates'iis:

1. The process of preparing luminescent .1nan'-' gane's'e-activated" zinc-beryllium silicate by the firingof a mixture of zinc, beryllium, silicon and 4. The "process accordingto claim 'l wherein the components zinc, beryllium'; silicon'and' mam ganese are'in the form' of thecorresponding oxides.

5. The process according tdclaim-IWhereinthe components zinc, beryllium, silicon and man-- ganese are in the forni-of the corresponding-car bonates.

J ACOBL-ROOSF REFERENCES CITED The following 'referencesare of re'cord'ifithei- Number Date Froelich June" 22, 1948' Certificate of Correction Patent No. 2,542,360 February 20, 1951 JACOB ROOS It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 3, line 32, after the Word beryllium insert oxide;

and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 17th day of April, A. D. 1951.

[SEAL] THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

1. THE PROCESS OF PREPARING LUMINESCENT MANGANESE-ACTIVATED ZINC-BERYLLIUM SILICATE BY THE FIRING OF A MIXTURE OF ZINC, BERYLLIUM, SILICON AND MANGANESE COMPONENTS OF THE GROUP CONSISTING OF THE OXIDES OF THOSE COMPONENTS AND MATERIALS WHICH UPON HEATING BREAK DOWN TO YIELD THE SAID OXIDES WHICH COMPRISES FIRING TO REACTION TEMPERATURE OF ABOUT 1000-1300* C. IN TWO SEPARATE STEPS, AT LEAST ABOUT HALF OF THE TOTAL BERYLLIUM COMPONENT BEING WITHHELD FROM THE MIXTURE DURING THE INITIAL FIRING STEP AND BEING SUBSEQUENTLY ADDED TO THE MIXTURE OF THE RE-FIRING STEP. 